LED is used for illuminating keyboard mainly because of the following reasons:

Power saving of LED bulbs

Power consumption is not more than 0.1w for each LED bulb. Commonly an illuminated keyboard only needs 10 LED bulbs for backlight.

Safe to use, friendly to environment

Material used to make LED bulb is safe to people. LED can also be recycled. It does not give out heat or radiation, making it safe to touch. It is green product for lighting.

Heat is a big issue for laptop computer. Too much heat may damage a laptop. Because LED bulb does not give out heat, it can be used in laptop keyboard for backlight. We can see that from Alienware laptop.

Strong level of lightness

For an illuminated keyboard, just 10 LED bulbs are enough for all the lighting. This is mainly because of the strong lightness of LED.

Long life of LED bulbs

Life of LED bulb is between 60,000 hours to 100,000 hours, which is really ten times of traditional light device.

Tiny size

Tiny size of LED bulbs makes it ideal for limited space inside a keyboard. This allows illuminated keyboard have ultra thin profile. The small LED bulbs can also be used in making illuminated keypad. 

Easy to replace

Even when a LED bulb in a keyboard is broken, it can be easily replaced.